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L-Per Direction Finding

L-Per Direction Finding. Modified from Hawk Mountain Civil Air Patrol 8-APR-06. Objectives. ELT Basics The Old Little L-Per DFing with the L-Per Hands-on Training. ELT Basics: The Flavors. ELT – Emergency Locator Transmitter aircraft EPIRB – Emergency Position Indicating Radio Beacon

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L-Per Direction Finding

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  1. L-Per Direction Finding Modified from Hawk Mountain Civil Air Patrol 8-APR-06

  2. Objectives • ELT Basics • The Old Little L-Per • DFing with the L-Per • Hands-on Training

  3. ELT Basics: The Flavors • ELT – Emergency Locator Transmitter • aircraft • EPIRB – Emergency Position Indicating Radio Beacon • boat • PLB – Personal Locator Beacon • hiker

  4. ELT Basics: The Flavors • No matter what you call it… • Transmits on a distress frequency • Indicates the position of an emergency by means of direction finding or GPS • Can be manually or automatically activated • Throughout this session, ELT will be used generically to also include PLBs & EPIRBs

  5. ELT Basics: The Frequencies • 121.5 MHz • Civilian Emergency Aircraft Channel • 243.0 MHz • Military Emergency Channel • 406 MHz • New Emergency Satellite Channel • ELTs can operate on just 1 or ANY combination of the above frequencies

  6. ELT Basics: Training Frequencies • To practice, we have our own set of frequencies: • 121.775 MHz • 121.6 MHz (No Longer Authorized) • 243.55 MHz (Proposed) • There is no 406 MHz training frequency

  7. 121.775 MHz Continuous Transmission Swept Tone ELT Basics: The Output

  8. The Old Little L-Per

  9. Controls • Mode Switch • Turns the unit OFF • Selects DF mode • Selects REC mode • The Mode switch determines how the L-Per operates

  10. Controls • Channel Switch • Selects the channel you wish to receive • If a position is blank – assume that there is no crystal installed • Units will have different channel options depending on which model your L-Per is

  11. Controls • Sensitivity • This control is used to reduce the sensitivity of the receiver. • Always start with this at MAX • Reduce as you get closer to your target (more details later)

  12. Controls • Volume • Set to a comfortable level • Keep as low as possible (and still hear the ELT) because… • Higher volumes reduce battery life • Volume has no effect on the indication on the meter

  13. Controls • Dial Light switch • Lights the meter • Keep off unless operating at night • Easy to bump the switch and not notice it in the daylight • Reduces battery life

  14. ALWAYS TURN A FULL CIRCLE BEFORE TAKING A COMPASS HEADING Use both REC and DF modes to verify the headings Hold the L-Per with two hands at a full arm’s length, keep the mast perpendicular to the ground Avoid power lines, large metal objects such as vehicles, buildings and signs when taking readings Keep other team members at least 10 feet away when trying to determine headings ALWAYS TURN A FULL CIRCLE BEFORE TAKING A COMPASS HEADING General Operation Notes

  15. If you can’t hear it… • If you can’t hear the ELT swept tone • You are too far away from the ELT • The ELT is broken • May be transmitting no audio or a continuous tone • There is no ELT transmitting • Unless you know for sure that the ELT is malfunctioning – don’t believe your L-Per readings

  16. Two Modes of Operation • The Little L-Per has two modes of operation • Each mode has its strengths and weaknesses • Always use both to determine a heading • Both modes should point you in the same direction, if not something’s up!

  17. REC = RECEIVE MODE More sensitive Allows you to take headings further away from the ELT No front/back ambiguity Less Accurate DF = DIRECTION FIND MODE Not as sensitive as REC Very accurate readings even at close range Front/back ambiguity exists More accurate headings than REC REC vs DF

  18. DF Mode • The meter tells you what DIRECTION THE ELT IS COMING FROM • Objective is to center the needle on the meter • Centered needle indicates the ELT is directly in front of or behind you

  19. DF Mode • Always turn in the direction the needle points • If the needle points right, turn right • If the needle points left, turn left

  20. DF Mode • When the needle centers, the ELT is directly in front of you or directly behind you • There is a way to determine if it’s in front of or behind you…

  21. DF Mode • To determine if the ELT is in front of or behind you… • Remember, the needle always points in the direction of the ELT • Turn slightly in one direction • If the needle moves in the OPPOSITE direction you are facing the ELT (re-center the needle before taking a compass heading) • If the needle moves in the SAME you were not facing the ELT, continue turning until the needle centers again, then re-check before taking the heading

  22. REC Mode • The meter tells you HOW STRONG THE SIGNAL IS • Objective is obtain maximum signal reading • Max meter reading is to the right of the meter • In REC Mode Strongest reading occurs when ELT is off the LEFT side of the antenna (YOUR LEFT when holding the L-Per)

  23. REC Mode Techniques • Start with Sensitivity at MAX • Reduce the Sensitivity so the needle is at mid-scale • Turn in a circle • Continue to turn in a circle – watch for meter readings that exceed mid-scale

  24. When a reading exceeds mid-scale, reduce the sensitivity to re-center the needle Keeping the highest reading at mid-scale makes it easy to determine if anything exceeds your previous highest reading Find the one spot that has the highest meter reading If you’ve followed this procedure, the highest reading you’ll see is mid-scale, everything else will be less than that At the highest meter reading, take a heading REC Mode Techniques

  25. What if… • You get more than 1 direction you feel the ELT is coming from? • You can hear the ELT but can’t get the L-Per to “tell” you a good heading? • REC and DF mode don’t agree?

  26. Then try… • Double check your instrument settings • Have someone else double check your instrument settings • Try a different location • You don’t have to move far (sometimes) • Radio waves at 121.5 MHz have a wavelength of about 8 feet

  27. IF you can’t hear the ELT… • If you can’t hear the ELT that means: • There is no ELT transmitting • You are too far from the ELT to hear it • The ELT is malfunctioning and not producing the swept tone • You or your L-Per are having difficulties… • As a general rule, if you can’t hear the ELT’s swept tone, you shouldn’t trust the L-Per’s meter readings

  28. The Old Little L-Per • The Old Little L-Per may produce needle movements with no ELT signal present • It may track random noise sources or interference from other radio transmitters

  29. Reflections & Propagation • Generally VHF radio waves travel in line of sight • The waves will reflect off of many objects • Its possible to get closer to the ELT and no longer be able to hear it

  30. Reflections & Propagation • Ideally radio waves propagate equally in all directions from an ELT antenna • Terrain, buildings, damage to the antenna can all cause the propagation to favor one direction over another

  31. How do you take a compass reading?

  32. Compass Heading • Once you determine what direction the ELT signal originates from • Take a compass heading • Record the information • Radio the information back to IC • Plot the heading on a map • IC will plot the heading on a map

  33. Compass Heading • A second person must be used to take the compass heading • The compass person should only approach the L-Per operator after the operator is sure of the ELT direction

  34. Compass Heading • The compass person needs to know whether the L-Per is in REC or DF Mode • How you measure the heading does not change between modes • How you interpret the heading does change

  35. Compass Heading in REC • Shoot your azimuth standing on the right of the L-Per operator • Sight your compass over both antennas • Your compass reading is the magnetic heading toward the ELT

  36. Compass Heading in DF • Shoot the azimuth standing on the right of the L-Per Operator • Sight your compass over the two antennas • Add 90 Degrees to the compass reading for the magnetic heading toward the ELT

  37. The unit runs on two 9v batteries – only 1 is needed for operation Old Little L-Per Tips ‘n Tricks

  38. The Future of ELTs Changes are in progress!

  39. Future of ELTs • COSPAS-SARSAT will no longer monitor 121.5 or 243 MHz as of: • February 1, 2009 • All ELTs must switch to 406 MHz • 406 MHz will be the only frequency monitored by the satellites • 406 MHz ELTs will also transmit on 121.5 and/or 243 MHz for local homing

  40. The New Little L-Per

  41. The New Little L-Per

  42. The New Little L-Per

  43. The New Little L-Per • Very similar in operation to the Old Little L-Per • The Sensitivity Control has been eliminated • Frequency Programmable • No Crystals to buy! • 108-174 MHz and 215-270 MHz standard • It floats!

  44. The New Little L-Per • The Old Little L-Per has not been available for some time • New purchases will likely be toward the New Little L-Per • Production started in early 2006 • Current price $750

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